Apparatus for measuring a mechanical quantity

ABSTRACT

A mechanical quantity measuring apparatus is provided which can make highly precise measurements and is not easily affected by noise even when it is supplied an electricity through electromagnetic induction or microwaves. At least a strain sensor and an amplifier, an analog/digital converter, a rectification/detection/modulation-demodulation circuit, and a communication control circuit are formed in one and the same silicon substrate. Or, the silicon substrate is also formed at its surface with a dummy resistor which has its longitudinal direction set in a particular crystal orientation and which, together with the strain sensor, forms a Wheatstone bridge. With this arrangement, even when a current flowing through the sensor is reduced, measured data is prevented from being buried in noise, allowing the sensor to operate on a small power and to measure a mechanical quantity with high precision even when it is supplied electricity through electromagnetic induction or microwaves.

BACKGROUND OF THE INVENTION

The present invention relates to an apparatus capable of measuring amechanical quantity and outputting a measured value wirelessly.

What is generally called an RF tag has been developed which uses anelectricity supplied through electromagnetic induction to active acircuit and thereby transmit a preset ID number wirelessly and which isbeginning to be applied to a goods distribution management and amanagement of admission tickets. Attempts are currently under way toconnect a physical quantity sensor to such an ID tag. For example, asdisclosed in JP-A-2001-187611, a temperature sensor is connected to anRF tag circuit on a printed circuit board, and the temperature sensormounted on the printed circuit board is then entirely molded withplastic to form an ID tag with a sensor.

BRIEF SUMMARY OF THE INVENTION

When a strain sensor and a mechanical quantity sensor applying thestrain sensor, such as pressure sensor, vibration sensor andacceleration sensor, are connected to a circuit that uses an electricitysupplied through electromagnetic induction or microwaves to transmit theresult of measurement, however, the following problems characteristic ofthe mechanical quantity sensor arise.

First, the strain sensor has a very small output for a measured strainand is very vulnerable to noise as compared with other sensors such astemperature sensor. For example, in normal use, the strain gauge isrequired to have a resolving power of the order of 10⁻⁵ and a resistancevariation (ΔR/R) in the most commonly used resistor wire type straingauge is about 2×10⁻⁵. That is, the strain gauge is required to detectwhen the resistor, whose resistance is 1 in a no-strain condition,produces a resistance of 1.00002 when strained. At this time, if anynoise, even at a small level, enters the circuit, it can cause largemeasuring errors. Particularly when the apparatus is operated on anelectric power supplied through electromagnetic induction or microwaves,the strain sensor is also subjected to a radio wave, making it easierfor the noise to enter the circuit. Further, when the electricitysupplied by electromagnetic induction or microwaves is used, an amountof electricity that can be supplied to the strain sensor is very limitedand is required to be set two or more orders of magnitude smaller thanwhen a commonly marketed strain gauge and an amplifier are used. Thus,if the current flowing through the strain sensor is set at a level ofthe order of μA, the apparatus becomes susceptible to noise, renderingthe measurements practically impossible without special considerations.The strain measurement is often made by directly attaching the sensor toan object being measured. Considering this condition of use, it isdifficult to cover the sensor and its lead wires with a conductivematerial for perfect electromagnetic shield. It is therefore an objectof this invention to provide a mechanical quantity measuring apparatuswhich is not susceptible to noise and can make highly precisemeasurements even when an electric power is supplied to the circuitthrough electromagnetic induction or microwaves.

A second problem is that the mechanical quantity sensor using asemiconductor has a larger temperature dependency of the measured valuethan other physical quantity sensors, so that unlike other sensors, themechanical quantity sensor is required to perform a temperaturecorrection. Normally, the strain sensor is combined with a dummyresistor having the same temperature dependency as the strain sensor toform a Wheatstone bridge circuit to perform the temperature correction.At this time, considerations must be taken to ensure that the dummyresistor and the sensor have the same temperatures. It is also necessaryto keep the dummy circuit in the bridge circuit in a non-strainedcondition. For this purpose, the dummy resistor and the sensor need tobe arranged separately and connected together. However, the lead wiresfor connection easily pick up noise, making the measurement practicallyimpossible without special considerations as in the case with the firstproblem. It is therefore an object of this invention to provide amechanical quantity measuring apparatus which is not susceptible tonoise and influences of temperature and can make highly precisemeasurements even when an electric power is supplied to the circuitthrough electromagnetic induction or microwaves.

To make the apparatus resistant to influences of noise even when a powerconsumption by the apparatus is lowered, a strain sensor takingadvantage of a piezoresistive effect and a circuit operating on anelectricity supplied by electromagnetic induction or microwaves areformed in the same silicon substrate.

Further, to make the apparatus resistant to temperature influences andto influences of noise even when a power consumption by the apparatus islowered, a Wheatstone bridge circuit is provided in the same singlecrystalline silicon substrate by forming an impurity diffusion layerwhose longer side lies in a particular direction.

For example, the mechanical quantity measuring apparatus may have formedin one main surface of a single crystal semiconductor substrate a strainsensor, an amplifying conversion circuit to amplify a signal from thestrain sensor and convert it into a digital signal, a transmissioncircuit to transmit the converted digital signal to the outside of thesemiconductor substrate, and a power circuit to supply in the form ofelectricity an electromagnetic wave energy received from outside thesemiconductor substrate.

Or the mechanical quantity measuring apparatus may have formed in onemain surface of a single crystal semiconductor substrate a Wheatstonebridge circuit made up of a strain sensor and a dummy resistor, aconversion circuit to amplify a signal from the Wheatstone bridgecircuit and convert it into a digital signal, a transmission circuit totransmit the digital signal to the outside of the semiconductorsubstrate, and a power circuit to supply in the form of electricity anelectromagnetic wave energy received from outside the semiconductorsubstrate.

Or the mechanical quantity measuring apparatus may have formed in onemain surface of a single crystal silicon substrate a Wheatstone bridgecircuit made up of a strain sensor and a dummy resistor, a conversioncircuit to amplify a signal from the Wheatstone bridge circuit andconvert it into a digital signal, a transmission circuit to transmit thedigital signal to the outside of the silicon substrate, a power circuitto supply electricity to these circuits according to a signalrepresenting at least one of vibrations, sunlight and temperaturedifference received from outside the silicon substrate, and a connectorto electrically connect power supply ground of one or more of thecircuits in the single crystal silicon substrate to an object beingmeasured.

This invention offers an advantage that, even when a mechanical quantitysensor is operated by using a small electricity supplied throughelectromagnetic induction or microwaves, noise picked up by the sensorcan be made very small. Since all the circuits are formed in a smallarea on the same silicon substrate, a current that would otherwise beinduced by a phase difference of radio waves when RF feeding (supply ofelectricity in the form of radio wave energy) is performed can beprevented from being generated in the sensor, making it possible for asensor to perform its intended sensing operation even when a smallelectric power is used. That is, when activating the circuits by usingan induced current as a power source, it is essential to reduce thepower consumption of the sensor. In that case, data from the sensor isnot buried in noise, allowing for correct measurement.

Further, since the Wheatstone bridge circuit of the above arrangementand construction is provided in the same single crystal siliconsubstrate, a small change in the resistance of the mechanical quantitysensor can be compensated for. Also, a good thermal conductivity of thesilicon substrate assures an accurate temperature correction and therebyimproves a measurement precision. Further, since a small strain sensorand a dummy resistor are formed in the same single crystal siliconsubstrate, noise does not easily enter the Wheatstone bridge circuit,preventing the measured data from being buried in noise even when thecurrent flowing in the sensor is reduced. This in turn makes for areduction in the power consumption of the sensor.

Furthermore, since the sensor's power consumption can be reduced, thisinvention enables the sensor to be operated with a small energy. Thismeans that the sensor can operate on an electric power supplied throughelectromagnetic induction or microwaves and also on electricity locallygenerated by vibrations and solar cells.

Other objects, features and advantages of the present invention willbecome more apparent from the following description of embodiments ofthe invention when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a perspective view of a mechanical quantity measuringapparatus as a first embodiment of this invention.

FIG. 2 is a perspective view showing how the mechanical quantitymeasuring apparatus as the first embodiment of the invention is used.

FIG. 3 is a perspective view showing how the mechanical quantitymeasuring apparatus as the first embodiment of the invention is used.

FIG. 4 is a perspective view of the mechanical quantity measuringapparatus as the first embodiment of the invention.

FIG. 5 is a perspective view of the mechanical quantity measuringapparatus as the first embodiment of the invention.

FIG. 6 is a perspective view of the mechanical quantity measuringapparatus as the first embodiment of the invention.

FIG. 7 is a perspective view of the mechanical quantity measuringapparatus as the first embodiment of the invention.

FIG. 8 is a perspective view of the mechanical quantity measuringapparatus as the first embodiment of the invention.

FIG. 9 is a perspective view of the mechanical quantity measuringapparatus as the first embodiment of the invention.

FIG. 10 is a perspective view of the mechanical quantity measuringapparatus as the first embodiment of the invention.

FIG. 11 is an explanatory diagram showing a Wheatstone bridge.

FIG. 12 is a perspective view of a mechanical quantity measuringapparatus as a second embodiment of the invention.

FIG. 13 illustrates a relation among a strain measuring direction, acrystal orientation of a silicon substrate, and a longitudinal directionof a diffusion layer in the mechanical quantity measuring apparatus asthe second embodiment of the invention.

FIG. 14 is a perspective view of the mechanical quantity measuringapparatus as the second embodiment of the invention.

FIG. 15 illustrates a relation among a strain measuring direction, acrystal orientation of the silicon substrate, and a longitudinaldirection of the diffusion layer in the mechanical quantity measuringapparatus as the second embodiment of the invention.

FIG. 16 is a perspective view of the mechanical quantity measuringapparatus as the second embodiment of the invention.

FIG. 17 illustrates a relation among a strain measuring direction, acrystal orientation of the silicon substrate, and a longitudinaldirection of the diffusion layer in the mechanical quantity measuringapparatus as the second embodiment of the invention.

FIG. 18 illustrates one example of arrangement of the diffusion layersand interconnects connecting the diffusion layers in the mechanicalquantity measuring apparatus as the second embodiment of the invention.

FIG. 19 illustrates another example of arrangement of the diffusionlayers and interconnects connecting the diffusions layer in themechanical quantity measuring apparatus as the second embodiment of theinvention.

FIG. 20 illustrates a relation among a strain measuring direction, acrystal orientation of the silicon substrate, and a longitudinaldirection of the diffusion layer in the mechanical quantity measuringapparatus as the second embodiment of the invention.

FIG. 21 illustrates a relation among a strain measuring direction, acrystal orientation of the silicon substrate, and a longitudinaldirection of the diffusion layer in the mechanical quantity measuringapparatus as the second embodiment of the invention.

FIG. 22 illustrates another example of arrangement of the diffusionlayers and interconnects connecting the diffusions layer in themechanical quantity measuring apparatus as the second embodiment of theinvention.

FIG. 23 is a perspective view of the mechanical quantity measuringapparatus as the second embodiment of the invention.

FIG. 24 illustrates another example of arrangement of the diffusionlayers and interconnects connecting the diffusion layers in themechanical quantity measuring apparatus as the second embodiment of theinvention.

FIG. 25 illustrates a relation among a strain measuring direction, acrystal orientation of the silicon substrate, and a longitudinaldirection of the diffusion layer in the mechanical quantity measuringapparatus as the second embodiment of the invention.

FIG. 26 illustrates another example of arrangement of the diffusionlayers and interconnects connecting the diffusion layers in themechanical quantity measuring apparatus as the second embodiment of theinvention.

FIG. 27 illustrates a relation among a strain measuring direction, acrystal orientation of the silicon substrate, and a longitudinaldirection of the diffusion layer in the mechanical quantity measuringapparatus as the second embodiment of the invention.

FIG. 28 illustrates another example of arrangement of the diffusionlayers and interconnects connecting the diffusion layers in themechanical quantity measuring apparatus as the second embodiment of theinvention.

FIG. 29 illustrates a relation among a strain measuring direction, acrystal orientation of the silicon substrate, and a longitudinaldirection of the diffusion layer in the mechanical quantity measuringapparatus as the second embodiment of the invention.

FIG. 30 illustrates another example of arrangement of the diffusionlayers and interconnects connecting the diffusion layers in themechanical quantity measuring apparatus as the second embodiment of theinvention.

FIG. 31 illustrates a relation among a strain measuring direction, acrystal orientation of the silicon substrate, and a longitudinaldirection of the diffusion layer in the mechanical quantity measuringapparatus as the second embodiment of the invention.

FIG. 32 illustrates a relation among a strain measuring direction, acrystal orientation of the silicon substrate, and a longitudinaldirection of the diffusion layer in the mechanical quantity measuringapparatus as the second embodiment of the invention.

FIG. 33 illustrates another example of arrangement of the diffusionlayers and interconnects connecting the diffusion layers in themechanical quantity measuring apparatus as the second embodiment of theinvention.

FIG. 34 illustrates a relation among a strain measuring direction, acrystal orientation of the silicon substrate, and a longitudinaldirection of the diffusion layer in the mechanical quantity measuringapparatus as the second embodiment of the invention.

FIG. 35 illustrates a Wheatstone bridge in the mechanical quantitymeasuring apparatus as the second embodiment of the invention.

FIG. 36 illustrates a Wheatstone bridge in the mechanical quantitymeasuring apparatus as the second embodiment of the invention.

FIG. 37 is a perspective view showing one chip formed with only a strainmeasuring unit in the mechanical quantity measuring apparatus as thesecond embodiment of the invention.

FIG. 38 is a perspective view showing the mechanical quantity measuringapparatus as the second embodiment of the invention having a self powergenerating unit.

FIG. 39 is a perspective view showing the mechanical quantity measuringapparatus as the second embodiment of the invention having a battery.

FIG. 40 is a schematic diagram showing a mechanical quantity measuringapparatus as a third embodiment of the invention having an ID memoryunit and capable of transmitting an ID value together with a measuredstrain value.

FIG. 41 is a schematic diagram showing the mechanical quantity measuringapparatus as the third embodiment of the invention having a self powergenerating unit.

FIG. 42 is a schematic diagram showing the mechanical quantity measuringapparatus as the third embodiment of the invention charging a batterywith a part of an energy of electromagnetic induction or microwaves andmeasuring a strain by using an electricity stored in the battery.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of this invention will be disclosed. A strain measuringsystem that operates on an electricity supplied by electromagneticinduction or microwaves can be formed on one and the same siliconsubstrate.

Embodiments of this invention will be described by referring to FIG. 1through FIG. 10. FIG. 1 shows a mechanical quantity measuring apparatus1 as a first embodiment of this invention. This embodiment is amechanical quantity measuring apparatus having formed on one and thesame single crystal silicon substrate 2 at least a strain sensor 3utilizing a piezoresistive effect, a strain sensor amplifier group 4, ananalog/digital converter 6, arectification/detection/modulation-demodulation circuit 7, acommunication control unit 8, a bonding surface 9, and an antenna 10. Inthe following description the silicon substrate 2 and a group of thinfilms formed on the silicon substrate 2 are together called a chip 101.Although the antenna 10 may be formed in large size outside the chip toreceive a greater amount of electricity, the following description takesup a case where the antenna is incorporated in the chip 101. When theantenna 10 is incorporated in the chip 101, the mechanical quantitymeasuring apparatus 1 constitutes the chip 101; and when an externalantenna is used, the combination of the chip 101 and the antenna 10 iscalled the mechanical quantity measuring apparatus 1. Incorporating theantenna in the chip 101 obviates the need for an electrode pad forexternal connection. This is desirable in terms of reliability becauseelectrodes are not exposed on the chip surface, protecting the electrodepad against corrosion even when used under severe environments. In thisembodiment, the chip 101 is bonded at the bonding portion to an object11 to be measured so that a strain is transmitted to the siliconsubstrate 2. When the silicon substrate 2 as a whole is loaded with astrain, a resistance of the strain sensor 3 in the silicon substrate 2changes and this resistance change is converted into a digital signalthrough the strain sensor amplifier group 4 and the analog/digitalconverter 6. The digital signal is then converted into a radio signalthrough the communication control unit 8 and therectification/detection/modulation-demodulation circuit 7 and sent fromthe antenna 10 to a leader. A high-frequency signal for electric powertransmitted from the leader is received by the antenna 10, smoothed bythe rectification/detection/modulation-demodulation circuit 7 into a DCpower of a constant voltage, which is then supplied as a power source tovarious circuits in the mechanical quantity measuring apparatus. Whilethis embodiment realizes an energy transmission by using anelectromagnetic induction that forms an induced electric field in theantenna or microwaves that are received and demodulated, it is possibleto utilize a mutual induction of coils for energy transmission or uselight for energy supply and communication.

The back of the silicon substrate is used as a bonding surface.

In the mechanical quantity measuring apparatus 1, a bonding surface 9 isformed at the back of the silicon substrate opposite the device formingsurface. As shown in FIG. 2, the mechanical quantity measuring apparatus1 is attached at its bonding surface 9 to the object 11 being measuredin order to measure a strain. In the mechanical quantity measuringapparatus 1, a strain can be measured by applying the strain through thebonding surface 9 to the entire silicon substrate in which variouscircuits are formed. Since the strain sensor 3 and its processingcircuits are highly integrated in the same silicon substrate, they canbe formed compact. It is preferred that the thickness of the siliconsubstrate be set less than or equal to 100 μm. In that case a strainvalue at the position of the strain sensor 3 can be made to match astrain value of the object 11. That is, keeping the thickness of thesilicon substrate 2 less than or equal to 100 μm can improve themeasuring accuracy. Forming the silicon substrate 2 in the thickness ofless than or equal to 100 μm offers another advantage that when theobject 11 being measured has a curved surface, the strain sensor 3 canbe bonded to the curved surface without being broken. Further, since thesilicon substrate 2 has a higher heat conductivity than an insulationfilm, the arrangement of the bonding surface 9 at the back of thesilicon substrate 2 allows the heat of the object 11 to be transmittedeasily to the strain sensor 3 on the front surface of the siliconsubstrate 2, offering an advantage of preventing an accuracy degradationthat would otherwise result from object temperature detection variationswhen a temperature correction is performed. Further, as the objecttemperature increases, with the sensor attached to the object 11, largeheat stresses may develop between the chip 101 and the object 11. Inthis invention, the silicon substrate 2 has the bonding surface 9 at theback and the back surface of the silicon substrate has a greater bondingstrength and fracture strength than the chip surface formed of, forexample, glass. Therefore, when the temperature of the object 11increases, the silicon substrate does not break or peel off at thebonding surface 9, assuring a reliable measurement. The bonding surface9 is formed by roughening the back surface of the silicon substrate andits roughness is set to more than 1 micron, which is larger than theroughness of the chip surface. This roughened surface produces ananchoring effect that improves the performance of bonding to the object11. As shown in FIG. 3 the chip 101 may be embedded in the object 11 tomeasure mechanical quantities. While this embodiment uses a siliconsubstrate, other semiconductor substrates may also be used whose surfaceis formed of single crystal.

Further, in this embodiment since the strain sensor 3, the strain sensoramplifier group 4 and the analog/digital converter 6 are formed in thesame silicon substrate and these circuits are interconnected in thechip, wires connecting the strain sensor 3 and other circuits can bemade very short, making noise entering the circuit extremely small evenwhen the apparatus is operated by using the electricity supplied throughthe electromagnetic induction or microwaves. When an induced current isused as a power supply to operate the circuits, it is essential toreduce the power consumption of the sensor. In this case also, thisembodiment can prevent sensor data from being buried in noise, assuringa correct measurement.

When only the strain sensor is attached to the object being measured,with other circuits formed separate from the sensor to avoid possibleinfluences of strain, however, the lead wire easily picks up noise whenradio waves from electromagnetic induction or microwaves are received.Thus the measure data is buried in noise, rendering the measurementpractically impossible without special considerations. This is caused bythe fact that since the sensor and other circuits are situated atseparate locations, a phase difference occurs between the sensor and theother circuits during the radio wave application, producing a signal ofa potential different from the original. In this embodiment, on theother hand, since a portion involved in the strain measurement can bedeemed almost as a point when compared with an expanse of the radiowaves, no phase difference is produced, making noise entering thecircuits very small, thus allowing for a correct measurement.

Next, the arrangement of the amplifier and the sensor will be explained.

In this embodiment, as shown in FIG. 4, the strain sensor 3 and thestrain sensor amplifier group 4 are formed adjacent to each other, andthe strain sensor amplifier group 4 and the analog/digital converter 6are formed adjacent to each other. Since the strain sensor 3 and thestrain sensor amplifier group 4 are arranged more close to each otherand the strain sensor amplifier group 4 and the analog/digital converter6 are also arranged more close to each other than to therectification/detection/modulation-demodulation circuit 7 and to thecommunication control unit 8, there is an advantage of the wires beingshort and noise not easily being picked up during radio waveapplication. Further, since this arrangement makes the strain sensor 3,strain sensor amplifier group 4, analog/digital converter 6 andtemperature sensor unit 12 quickly become uniform in temperature, thereis an advantage that the apparatus is not easily affected by temperaturedrifts.

Further, if the strain sensor is arranged at an end portion of the chip101, a stress in the surface of the chip 101 may become ununiform.Particularly at the end portion of the chip, measured values may belargely different from the actual strain of the object, so it is desiredthat the strain sensor be put closer to the central portion of the chipthan the rectification/detection/modulation-demodulation circuit 7, thecommunication control unit 8 and the antenna 10. That is, as shown inFIG. 5, a distance from the strain sensor 3 to a rotationally symmetricaxis or the center of the chip is preferably shorter than that from therectification/detection/modulation-demodulation circuit 7, thecommunication control unit 8 and antenna 10 to the rotationallysymmetric axis or the center of the chip.

Particularly, since the antenna 10 is a relatively large structure inthe chip, it may cause a strain nonuniformity in a plane. Thus, as shownin FIG. 1 and FIGS. 4 to 6, the antenna 10 is preferably arranged alongthe periphery of the chip 101 with the strain sensor placed inside theantenna. This also applies when a coil of the antenna 10 is woundseveral times, as shown in FIG. 6. Further, when the antenna 10 is anexternal antenna and formed of a film outside the silicon chip, theabove arrangement produces the similar effect.

The sensor is arranged so that its longitudinal direction matches thelongitudinal direction of other devices.

Further, in this embodiment, the longitudinal direction of resistors 26used in a feedback circuit of the strain sensor amplifier group 4 shownin FIG. 7 is preferably arranged as close to the strain measuringdirection as possible, as shown in FIG. 8. For example, if thelongitudinal direction of the resistors 26 is set perpendicular to thestrain measuring direction and when even a small force is applied in thedirection perpendicular to the strain measuring direction, theamplification factor changes greatly, producing large measuring errors.On the other hand, if the longitudinal direction of the resistors 26 isset parallel to the strain measuring direction, a sensitivity becomessmall in a direction perpendicular to the strain measuring direction. Itis noted, however, that since there is a sensitivity in the longitudinaldirection of the resistors 26, the amplification factor slightly variesdepending on the strain. This can be corrected by applying a knownstrain and using the corresponding measured value of the mechanicalquantity measuring apparatus 1, thus assuring a highly accuratemeasurement. The similar effect can also be produced in a case where thechip includes only the strain sensor amplifier group 4 and the strainsensor 3, with the rectification/detection/modulation-demodulationcircuit 7 and the communication control unit 8 removed. When theamplifier feedback resistors are formed of a diffusion resistor in thesilicon substrate or when CMOS circuits and bipolar amplifiers areformed, the longitudinal direction of their current paths is set almostin <100> to make them less vulnerable to the influences of strains, thusassuring highly accurate measurement. According to the usage of thisapparatus, this embodiment positively applies large strains to theapparatus. Thus, by lowering the strain sensitivity in other than thestrain sensor, a highly precise measurement can be made.

It is preferred that the chip and the object being measured be set atthe same potential.

It is also desired that the object 11 be electrically connected, eitherthrough DC or AC component, to the power supply ground of the chip 101.That is, the power supply ground of the chip 101 and the object 11 maybe electrically connected or they may be electrically coupled by an ACcomponent through a thin insulating film. As a result, the object 11 andthe chip 101 have the same potential, so that the energy transmissionefficiency can be improved when an electromagnetic energy is used as apower source or when radio waves are transmitted.

The strain measuring direction is preferably marked on the chip.

This embodiment is characterized in that the strain measuring directionis marked on the chip, as shown in FIG. 9. The strain sensor in the chipis often as small as several tens of microns in size and the strainsensor, and the other circuits are formed in the same silicon substrate.Thus, the direction of the gauge cannot be seen as in the conventionalstrain gauges. It is therefore necessary to attach a mark 15representing the strain measuring direction according to the directionof the diffusion layer 14 in the silicon substrate surface that senses astrain.

Since the longitudinal direction of the diffusion layer 14 in thesilicon substrate surface that senses a strain is the strain measuringdirection, the chip is marked at 15 for the user to be able to recognizethat direction. This mark 15 is preferably made in the form of a thinfilm formed near the surface of the chip 101 or in the form of a scar onthe silicon chip. This mark 15 may be used in combination with thefunction of the antenna 10 and need only be a thin film large enough tobe recognized by the user. Further, as shown in FIG. 10, the mark 15 maybe provided at two locations, front and rear.

A second embodiment of this invention will be explained by referring toFIG. 11 through FIG. 39. Although the mechanical quantity measuringapparatus of this embodiment has basically the same construction andfeature as the first embodiment, it is characterized in that aWheatstone bridge 16 made up of strain sensors 3 and dummy resistors 17is formed in the same single crystal silicon substrate that incorporatesother circuits. Although the dummy resistors 17 may also have a smallstrain sensitivity, they are called dummy resistors 17 for the sake ofexplanation.

A circuitry of the Wheatstone bridge is shown in FIG. 11. Since thestrain sensor 3 has a very small change in resistance caused by strain,simply amplifying the strain as is will make the signal processing atlater stages complex. Thus, as in normal use of a strain gauge, it isoften a common practice to form a Wheatstone bridge circuit 16 toproduce an output voltage proportional to a change in the resistance ofthe strain sensor 3 and then to amplify the output voltage and use it asa value proportional to the strain. If a temperature dependence of theresistance of the dummy resistor 17 is set equal to that of the strainsensor 3, their temperatures can be made equal, thereby enabling thetemperature correction of the strain sensor 3. At this time, the dummyresistors 17 in the Wheatstone bridge 16 must not be attached to theobject in order to keep them in a no-strain state. The dummy resistor 17has a smaller resistance change than the strain sensor 3 when subjectedto strain.

However, when it is attempted to form the Wheatstone bridge 16 in themechanical quantity measuring apparatus, a grave problem arises. Sincethe mechanical quantity measuring apparatus has various circuits formedin the same single crystal silicon substrate 2 and is bonded to theobject through the bonding surface 9 at the back of the siliconsubstrate, other circuits than the strain sensor 3 are also affected bythe strain. This means that forming the Wheatstone bridge 16 on the samesilicon surface causes almost the same resistance change in the dummyresistor 17 as the strain sensor 3, making the correct measurementimpossible.

FIG. 12 shows a mechanical quantity measuring apparatus having theWheatstone bridge 16 of this embodiment that can avoid the aboveproblem. In the Wheatstone bridge 16, the strain sensor 3 is formed bylocally diffusing a p-type impurity layer into the silicon substrate 2and has its longitudinal direction in <110>. The dummy resistor 17 issimilarly formed by locally diffusing a p-type impurity layer into thesilicon substrate. The dummy resistor 17 is V-shaped as shown in FIG. 12and is arranged so that longitudinal straight line segments of theV-shaped dummy resistor 17 extend in <100> direction. Further, thestrain sensor 3 and the dummy resistor 17 are formed in a way that makestheir resistances almost equal. The dummy resistor 17 is bent such thatthe two straight line segments of the V shape are equal in length.

FIG. 13 shows a relation between the shapes of the strain sensor 3 andthe dummy resistor 17 and a crystal orientation of the silicon substrate2. Constructing the strain sensor 3 of the p-type impurity diffusionlayer and arranging its longitudinal direction in <110> direction offersthe advantage of increasing the strain sensitivities in the longitudinaldirection and a direction perpendicular to it. That is, it is possibleto measure the strains in these directions with higher priority. Here,the longitudinal direction may be interpreted as the direction in whichan electric current flows. It is also possible to fold the impuritydiffusion layer to form the strain sensor 3 and the dummy resistor 17.In that case, too, the longitudinal direction can be considered to be adirection in which the current flows in the diffusion layer. While <110>is taken to be the longitudinal direction, it may slightly deviate fromthe longitudinal direction to produce the similar effect but with anincreased error. Further, by forming the dummy resistor 17 of the p-typeimpurity diffusion layer and setting the longitudinal direction in <100>direction, the sensitivity for a vertical strain can be minimized. Andforming the dummy resistor 17 in the V shape can cancel the sensitivityfor an in-plane shearing strain, further lowering the sensitivity of thedummy resistor 17. Further, since both of the strain sensor 3 and thedummy resistor can be constructed of the same p-type impurity layer,they can be formed simultaneously in the same process and thereby givenalmost equal resistances. For example, performing the ion implantationof the p-type impurity for both of them at the same time to form theirimpurity layers results in the strain sensor 3 and the dummy resistor 17having almost equal sheet resistances. As a result, an offset of anoutput from the Wheatstone bridge circuit can be minimized withoutconsidering variations in manufacturing process. In that case, theimpurity diffusion processing is preferably performed during an ionimplantation process and a subsequent activation process because theaccuracy of impurity dose is high and a diffusion profile has goodreproducibility. Further, since the strain sensor and the dummy resistorcan be made to have the same sheet resistances by forming them of thesame p-type impurity layer at one time, their temperature dependenciesof resistance can be made almost equal. If a design is made in which theimpurity concentrations in the strain sensor and the dummy resistor arenot equal, the similar effects to those described above can also beproduced although there is some possibility of small errors occurring inthe temperature correction and resistance deviations of the strainsensor 3 and the dummy resistor 17 are expected to vary. Rather thanconstructing the dummy resistor 17 of V-shaped diffusion layer, it ispossible to connect together, through wires, diffusion layers whoselongitudinal direction lies in <100> direction as shown in FIG. 14, inorder to produce the same resultant effect. In that case, it is desiredthat the resistance value of the connected diffusion layers of the dummyresistor 17 be equal to that of the strain sensor 3. This arrangementoffers an advantage that the layout of the strain sensor and the dummyresistor can be made freely. FIG. 15 shows an arrangement of diffusionlayers and connections of bridge wires 18 when the construction of thediffusion layers of FIG. 14 is employed. The example shown in FIG. 15considers the arrangement of the diffusion layers and the bridge wires18 so that the lengths of bridge wires are equal as practically aspossible. The diffusion layers may be arranged such that, as shown inFIG. 12 and FIG. 14, the V-shaped dummy resistors 17 may open in thesame direction. This arrangement has the advantage of being able toreduce an area occupied by the Wheatstone bridge circuit 16. While inFIG. 12, FIG. 14 and FIG. 15 the two strain sensors 3 are arrangedspaced apart with a group of dummy resistors 17 in between, they may bearranged parallel. This arrangement also can reduce the occupied area.Arranging the bride wires so as not to collapse a mirror symmetry likethat of the bridge wires 18 of FIG. 15 can keep the bridge wires 18 fromdiffering in length from one another greatly, thereby reducingresistance deviations of the four bridges.

Further, when the dummy resistors are arranged linearly as shown in FIG.16, not in the V-shaped configuration, the similar effects as describedabove can also be produced although they become slightly moresusceptible to the influences of in-plane shearing force. FIG. 17 showsa relation between the shapes of the strain sensor 3 and the dummyresistor 17 and the crystal orientation of the silicon substrate 2.Forming the strain sensor 3 of a p-type impurity diffusion layer andsetting a <110> direction as the longitudinal direction has theadvantage of increasing the strain sensitivity in the longitudinaldirection and in a direction perpendicular to it. The sensitivity forthe vertical strain can be minimized by forming the dummy resistor of ap-type impurity diffusion layer and setting the longitudinal directionin <100> direction.

Although this method cannot cancel the in-plane shearing components, ithas the advantage of simplifying the layout because the dummy resistor 7is not arranged in a V-shaped configuration. Forming the dummy resistor7 in the V-shaped configuration and matching the resistance value tothat of the strain sensor 3 with high precision is difficult to achieve.In this respect, the method shown in FIG. 17 is simple and can match theresistance value of the dummy resistor 7 to that of the strain sensor 3with high precision. An example of FIG. 18 considers the diffusionlayers and the bridge wires 18 in a way that can make the bridge wires18 as equal in length as possible.

While in the above explanation the strain sensor has been described tobe formed in <110> direction and the dummy resistor in <100> direction,it should be noted that this is an ideal state and that theabove-described effect can be produced even if there are some deviationsin angle. That is, the above-described effect can be obtained byorienting the strain sensor in a direction closer to <110> than <100>and the dummy resistor in a direction closer to <100> than <110>.

FIG. 19 shows an example arrangement when the silicon substrate 2 andthe dummy resistor 17 are formed of an n-type impurity diffusion layer.FIG. 20 shows a relation between the shapes of the strain sensor 3 anddummy resistor 17 and the crystal orientation of the silicon substrate2. In this case, the strain sensor 3 and the dummy resistor 17 areformed so that the longitudinal direction of the strain sensor 3 lies in<100> and that of the dummy resistor 17 lies in <110>. When a V-shapeddummy resistor 17 is used to cancel the in-plane shearing components, asshown in FIG. 21 and FIG. 22, a highly accurate measurement is possiblebecause the dummy resistor 17 is not easily influenced by multi-axisstrain components. When the strain sensor 3, such as shown in FIG. 19,FIG. 20, FIG. 21 and FIG. 22, is used, the strain measuring direction is<100>. That is, the strain sensor 3 can measure mainly the strains inthe longitudinal direction of the diffusion layer that forms the strainsensor 3 and also those in a direction perpendicular to the longitudinaldirection. Therefore, the mark 15 representing the strain measuringdirection is formed either toward the <100> direction, i.e.,longitudinal direction of the diffusion layer, or the directionperpendicular to it, or toward both directions. When circuits and wiresare formed in directions perpendicular to and parallel to the <110>directions as in ordinary semiconductor devices, the strain measuringdirection is hardly identifiable by the user. So, the mark 15 ispreferably formed as shown in FIG. 23, for example.

As described above, when the strain sensor 3 and the dummy resistor 17are formed using n-type impurity diffusion layers, there is an advantagethat the manufacturing process becomes simple when other circuits arealso formed of n-type semiconductor devices although the sensitivityslightly lowers as compared with a case where a p-type impuritydiffusion layer is used. This is because the use of n-type semiconductordevices also in other circuits obviates the need for diffusing p-typeimpurities in order to form only the strain sensor 3. Further, thesilicon crystal has a cleavage surface in <111> direction, and thereforesetting the strain measuring direction in <100> offers the advantagethat the silicon crystal does not easily crack when measuring largestrains.

FIG. 24 shows an example arrangement when the strain sensor 3 is formedof a p-type impurity diffusion layer and the dummy resistor 17 is formedof an n-type impurity diffusion layer. FIG. 25 shows a relation betweenthe shapes of the strain sensor 3 and dummy resistor 17 and the crystalorientation of the silicon substrate 2. In this case, both of the strainsensor 3 and the dummy resistor 17 are formed so that their longitudinaldirection lies in <110> direction and the strain measuring direction isalso <110>. In this example, the p-type impurity diffusion layer thatforms the strain sensor 3 exhibits a resistance change of positive signfor a strain change of positive sign in the strain measuring direction.The n-type impurity diffusion layer that forms the dummy resistor 17, onthe other hand, exhibits a resistance change of negative sign for astrain change of positive sign in the strain measuring direction. Thisoffers an advantage that, compared with a bridge circuit having alow-sensitivity dummy resistor, a high output is produced, increasingthe sensitivity. Further, since the strain sensor 3 and the dummyresistor 17 are formed parallel, this arrangement has another advantageof being able to reduce an area occupied by the Wheatstone bridge 16.This in turn reduces an overall chip size and therefore the cost.

Further, FIG. 26 shows an example arrangement in which the strain sensor3 is formed of an n-type impurity diffusion layer and the dummy resistor17 is formed of a p-type impurity diffusion layer. FIG. 27 shows arelation between the shapes of the strain sensor 3 and the dummyresistor 17 and the crystal orientation of the silicon substrate 2. Inthis case, the strain sensor 3 and the dummy resistor 17 are formedalmost parallel, with their longitudinal direction lying in <100>. Thestrain measuring direction is also <100>. In this example, the strainsensor 3 formed of an n-type impurity diffusion layer is arranged in adirection that maximizes the sensitivity for vertical strain. On theother hand, the dummy resistor 3 formed of a p-type impurity diffusionlayer has the lowest sensitivity in all directions among the n- andp-type impurity diffusion layers that can be formed in a (001) plane.This arrangement therefore allows for a precise measurement. Further,since the strain sensor 3 and the dummy resistor 17 are formed parallel,the area occupied by the Wheatstone bridge 16 can be reduced.

FIG. 28 shows an example arrangement in which the strain sensor 3 isformed of an n-type impurity diffusion layer and the dummy resistor 17is formed of a p-type impurity diffusion layer. FIG. 29 shows a relationbetween the shapes of the strain sensor 3 and the dummy resistor 17 andthe crystal orientation of the silicon substrate 2. In this case, thestrain sensor 3 is formed so that its longitudinal direction lies in<100> and the dummy resistor 17 is formed so that its longitudinaldirection lies in <110>. In this arrangement, the direction in which themaximum sensitivity is obtained is also <100>. Since the sensitivity ofthe strain sensor 3 in the <100> direction is high and the sensitivityof the dummy resistor 17 for various strain components is low, a highlyprecise measurement can be made.

Further, it is possible to form the strain sensor and the dummy resistorso that their diffusion layers extend almost perpendicularly to eachother, as shown in FIG. 34. In this case, the strain sensor 3 and thedummy resistor 17 have equivalent sensitivities but they are called thestrain sensor 3 and the dummy resistor 17 for a convenience sake. Thisembodiment has as high a strain sensitivity in a direction perpendicularto the longitudinal direction of the strain sensor 3 as in thelongitudinal direction. There is an advantage that the strainsensitivities are twice those of FIG. 18 and FIG. 19. This arrangement,however, has a drawback that resistance variations and sensitivityvariations of the strain sensor 3 and the dummy resistor 17 are greatlyreflected on the measurement, increasing measurement variations. Anotherdisadvantage is that the occupied area is larger than those shown inFIG. 18 and FIG. 19. Although FIG. 34 shows an example case in which ap-type impurity diffusion layer is used, an n-type impurity diffusionlayer may also be used. In that case, the impurity diffusion layers needto be formed so that their longitudinal directions lie in <110>. It isalso possible to combine the n-type impurity diffusion layer and thep-type impurity diffusion layer.

Next, a Wheatstone bridge circuit that can take measurements of only ashearing strain will be explained.

FIG. 30 shows an example arrangement in which the strain sensor 3 andthe dummy resistor 17 are formed of a p-type impurity diffusion layer.FIG. 31 shows a relation between the shapes of the strain sensor 3 anddummy resistor 17 and the crystal orientation of the silicon substrate2. In this case, the strain sensor 3 is formed so that its longitudinaldirection lies in <100> and the dummy resistor 17 is formed so that itslongitudinal direction lies in <110>. In an x-y coordinate system, suchas shown in FIG. 30, this arrangement allows a shearing strain τ_(xy) tobe measured.

Further, FIG. 32 shows an example arrangement in which the strain sensor3 and the dummy resistor 17 are formed of an n-type impurity diffusionlayer. FIG. 33 shows a relation between the shapes of the strain sensor3 and dummy resistor 17 and the crystal orientation of the siliconsubstrate 2. In this case, the strain sensor 3 is formed so that itslongitudinal direction lies in <100> and the dummy resistor 17 is formedso that its longitudinal direction lies in <110>. In an x-y coordinatesystem, such as shown in FIG. 33, this arrangement allows a shearingstrain T_(xy) to be measured. That is, this arrangement has an advantagethat the sensitivity is small for vertical strain components and highfor only T_(xy). By bonding this apparatus to a rotating shaft, a shafttorque can be measured.

FIG. 35 shows how another Wheatstone bridge circuit of this embodimentis constructed. In this embodiment, the circuit comprises one strainsensor 3 and three dummy resistors 17. Although the strain sensitivityin this case degrades to half that of the circuit shown in FIG. 11, thiscircuit can produce the similar effects to that of FIG. 11. FIG. 36shows a circuit made up of three strain sensors 3 and one dummy resistor17. In this case, too, the circuit can produce the similar effects tothat of FIG. 11 although the strain sensitivity falls to half that ofthe circuit shown in FIG. 11. The relation between the shapes of thestrain sensor 3 and dummy resistor 17 and the crystal orientation of thesilicon substrate 2 can apply the combinations shown in FIG. 12 throughFIG. 34. As to the arrangement of the strain sensor 3 and the dummyresistor 17, it is desirable to arrange the strain sensor and the dummyresistor as close to each other as possible, considering the problem oftemperature uniformity.

The sensor may be used as a single device.

The embodiment having the Wheatstone bridge shown in FIG. 12 to FIG. 36formed on the silicon substrate 2 can be used as a single strain sensor,as shown in FIG. 37. The strain sensor having the Wheatstone bridge 16of this embodiment formed on the same silicon substrate 2 obviates theneed for installing the Wheatstone bridge outside the silicon substrate2 as is done in the common measurement using the ordinary strain gauge.Further, since the Wheatstone bridge is connected to other circuitsthrough the silicon substrate, its heat conduction is good allowing foreasy temperature compensation. Further, since it is fabricated by asemiconductor manufacturing process, the sensor unit can be formedsmall, which in turn enables the measurement of strain in small parts.Since the silicon substrate 2 and the dummy resistor 17, that togethermake up the Wheatstone bridge, are concentratedly formed in a very smallarea on one silicon substrate, the noise resistance of the circuit isexcellent.

The above Wheatstone bridge can also be applied similarly to a chiphaving a self power generating unit 19, as shown in FIG. 38. In thiscase, too, since the circuit of this invention operates on a small powerand is little affected by external disturbances (noise), it can also beapplied to apparatus that can self-generate only a small power. Forexample, when the self power generating unit 19 transforms vibrationsinto energy, the apparatus can measure strains even where vibrations aresmall. Further, in an apparatus having a solar cell mounted as the selfpower generating unit 19, strain measurements can be made at locationswhere illumination level is low. Further, in a chip that is suppliedelectricity from a battery 20 as shown in FIG. 39, since this inventioncan prolong the life of the battery 20, the measurement of mechanicalquantities can be made for a long period of time. Although FIG. 39 showsthe construction in which the battery 20 is built into the chip, thebattery 20 may be installed outside the chip. In that case, a battery 20of larger capacity can be installed allowing for a longer period of use.

A third embodiment of this invention will be explained by referring toFIG. 40 to FIG. 42. FIG. 40 shows a mechanical quantity measuringapparatus of this embodiment. This apparatus has the similarconstruction to those of the first and second embodiment and can alsotransmit an ID number. This apparatus is characterized by an ID memoryunit 21 storing an ID number. A radio wave transmitted from areader/writer is received and smoothed by this apparatus which then usesthe smoothed electricity as a power source to operate the strain sensor3 and the strain sensor amplifier group 3. A resistance change that isread and amplified is converted by an analog/digital converter 12 into adigital value, which is then temporarily stored in a register 22together with the ID number supplied from the ID memory unit 21, andthen transmitted through a communication control unit 8 and arectification/detection/modulation-demodulation circuit 7. With thisembodiment, since the reader/writer can receive the ID number togetherwith the measured strain value, the management of measurements can befacilitated. For example, since strains at various locations can bemanaged based on the ID numbers, it is possible to check changes ofstrain over time at any particular location with ease.

FIG. 41 shows a configuration of another mechanical quantity measuringapparatus, which has a self power generating unit allowing for ameasurement of a mechanical quantity even when the apparatus is notreceiving a radio wave from the reader/writer. It also incorporates anonvolatile memory 23 that can store the strain value permanently. Ifthe nonvolatile memory 23 is made to store strain values larger than apreset value, a history of only large loads can be kept. This can reducethe required memory capacity and therefore enables the apparatus to beoperated with a small generated power. A timer 24 is built into theapparatus. This offers an advantage of being able to store time, loadand ID number at the same time. The measured values accumulated in thenonvolatile memory 23 can be read out through electromagnetic inductionor microwaves. That is, since transmitting the measured values throughradio waves requires a large electric power, the energy for radio wavetransmission is supplied by the electromagnetic induction or microwaves.The energy for the measurement that does not require a large amount ofelectricity is supplied by the self generated power. With thisinvention, it is possible to reduce power consumption of the strainsensor 3 and thus realize a mechanical quantity measuring apparatusshown in FIG. 41. That is, since the transmission of radio wave ispowered by the electromagnetic induction or microwaves and the powerconsumption of the sensor is reduced, the measurement can be made at alltimes even when the power produced by the self power generating unit 19is small. Here, the self power generating unit 19 includes a battery andperforms a vibration power generation, a solar power generation, a powergeneration using piezoelectric elements, and a power generation usingfluid force. As described above, this embodiment has a great advantagethat the apparatus can be operated even in applications where an outputof the self power generating unit 19 is small.

FIG. 42 shows an example configuration of a measuring apparatus which ispowered by electromagnetic induction or microwaves and which introducesa part of the received power to a battery 25 for charging. Since thisinvention can reduce the power required for sensing to a very smalllevel, strain can be measured at all times or intermittently by usingpower from the battery 25. Transmitting a measured value over a radiowave requires a sufficient power, so the apparatus is suppliedelectricity through radio wave when reading the measured value, as inthe first embodiment. At the same time, the battery 25 is also charged.With this invention, since the power consumption of the strain sensor 3can be reduced, the amount of electricity required to be charged alsodecreases, making it possible to realize the mechanical quantitymeasuring apparatus shown in FIG. 42.

While the invention has been described by taking up example embodiments,it is apparent to those skilled in the art that this invention is notlimited to these embodiments and that various modifications and changesmay be made without departing from the spirit of this invention andwithin the scope of appended claims.

1. A mechanical quantity measuring apparatus having formed in one main surface of a single crystal semiconductor substrate: a strain sensor; an amplification conversion circuit to amplify a signal from the strain sensor and convert it into a digital signal; a transmission circuit to transmit the converted digital signal to the outside of the semiconductor substrate; and a power supply circuit to supply as electricity an electromagnetic wave energy received from the outside of the semiconductor substrate.
 2. A mechanical quantity measuring apparatus having formed in one main surface of a single crystal semiconductor substrate: a Wheatstone bridge circuit made up of a strain sensor and a dummy resistor; a conversion circuit to amplify a signal from the Wheatstone bridge circuit and convert it into a digital signal; a transmission circuit to transmit the digital signal to the outside of the semiconductor substrate; and a power supply circuit to supply as electricity an electromagnetic wave energy received from the outside of the semiconductor substrate.
 3. A mechanical quantity measuring apparatus having formed in one main surface of a single crystal silicon substrate: a Wheatstone bridge circuit made up of a strain sensor and a dummy resistor; a conversion circuit to amplify a signal from the Wheatstone bridge circuit and convert it into a digital signal; a transmission circuit to transmit the digital signal to the outside of the silicon substrate; a power supply circuit to supply electricity to these circuits based on at least one of vibrations, sunlight and temperature differences received from the outside of the silicon substrate; and a connector to electrically connect a power supply ground of any of the circuits on the single crystal silicon substrate to an object to be measured.
 4. A mechanical quantity measuring apparatus according to claim 2, wherein the single crystal silicon substrate is 100 μm or less thick.
 5. A mechanical quantity measuring apparatus according to claim 3, wherein the power supply circuit supplies as electricity an electromagnetic wave energy received from the outside of the silicon substrate to any of the circuits; wherein a back of the main surface of the single crystal silicon substrate is formed with a bonding surface for bonding to the object to be measured.
 6. A mechanical quantity measuring apparatus according to claim 3, wherein the power supply circuit supplies as electricity an electromagnetic wave energy received from the outside of the silicon substrate to any of the circuits; wherein a visible mark is formed in a strain measuring direction.
 7. A mechanical quantity measuring apparatus having formed in a surface of a single crystal silicon substrate: a Wheatstone bridge circuit made up of a strain sensor and a dummy resistor; a temperature sensor; a conversion circuit to amplify a signal from the Wheatstone bridge circuit and the temperature sensor and convert it into a digital signal; a transmission circuit to transmit the digital signal to the outside of the silicon substrate; and a power supply circuit to supply as electricity an electromagnetic wave energy received from the outside of the silicon substrate to any of the circuits.
 8. A mechanical quantity measuring apparatus having formed in a surface of a single crystal silicon substrate: a Wheatstone bridge circuit made up of a strain sensor and a dummy resistor; a conversion circuit to amplify a signal from the Wheatstone bridge circuit and convert it into a digital value; a transmission circuit to transmit the digital value and an ID number stored in a ROM to the outside of the silicon substrate; and a power supply circuit to supply as electricity an electromagnetic wave energy received from the outside of the silicon substrate to any of the circuits.
 9. A mechanical quantity measuring apparatus having formed in a surface of a single crystal silicon substrate: a Wheatstone bridge circuit made up of a strain sensor and a dummy resistor; a conversion circuit to amplify a signal from the Wheatstone bridge circuit and convert it into a digital signal; a transmission circuit to transmit the digital signal to the outside of the silicon substrate; and any of a vibration power generation unit, a solar power generation unit and a temperature difference power generation unit provided outside the single crystal silicon substrate to electrically connect to any of the circuits.
 10. A mechanical quantity measuring apparatus according to claim 1, wherein the electromagnetic wave energy is a radio wave.
 11. A mechanical quantity measuring apparatus having formed in a surface of a single crystal silicon substrate a Wheatstone bridge circuit made up of a strain sensor and a dummy resistor; wherein the strain sensor has in the silicon substrate a region into which a p-type impurity layer is diffused; wherein the strain sensor has its longitudinal direction set in <110> direction; wherein the dummy resistor has in the silicon substrate a region into which a p-type impurity layer is diffused; wherein the dummy resistor has its longitudinal direction set in <100> direction.
 12. A mechanical quantity measuring apparatus having formed in a surface of a single crystal silicon substrate a Wheatstone bridge circuit made up of a strain sensor and a dummy resistor; wherein the strain sensor has formed in the silicon substrate a region into which an n-type impurity layer is diffused; wherein the n-type region has its longitudinal direction set in <100> direction; wherein the dummy resistor has formed in the silicon substrate a region into which an n-type impurity layer is diffused; wherein the p-type region has its longitudinal direction set in <110> direction.
 13. A mechanical quantity measuring apparatus having formed in a surface of a single crystal silicon substrate a Wheatstone bridge circuit made up of a strain sensor and a dummy resistor; wherein the strain sensor is formed of a p-type impurity diffusion layer and the dummy resistor is formed of an n-type impurity diffusion layer; wherein both of the strain sensor and the dummy resistor have their longitudinal directions set in <110> direction.
 14. A mechanical quantity measuring apparatus having formed in a surface of a single crystal silicon substrate a Wheatstone bridge circuit made up of a strain sensor and a dummy resistor; wherein the strain sensor is formed of an n-type impurity diffusion layer and the dummy resistor is formed of a p-type impurity diffusion layer; wherein both of the strain sensor and the dummy resistor have their longitudinal directions set in <100> direction.
 15. A mechanical quantity measuring apparatus having formed in a surface of a single crystal silicon substrate a Wheatstone bridge circuit made up of a strain sensor and a dummy resistor; wherein the strain sensor is formed of an n-type impurity diffusion layer and the dummy resistor is formed of a p-type impurity diffusion layer; wherein the strain sensor has its longitudinal direction set in <100> direction and the dummy resistor have its longitudinal direction set in <110> direction.
 16. A mechanical quantity measuring apparatus having formed in a surface of a single crystal silicon substrate: at least, a Wheatstone bridge circuit made up of a strain sensor and a dummy resistor; a conversion circuit to amplify a signal from the Wheatstone bridge circuit and convert it into a digital signal; a transmission circuit to transmit the digital signal to the outside of the silicon substrate; and a circuit to supply as electricity an electromagnetic wave energy received from the outside of the silicon substrate to any of the circuits; wherein the strain sensor is formed by locally diffusing a p-type impurity layer into the silicon substrate; wherein the strain sensor has its longitudinal direction set in <110> direction wherein the dummy resistor is formed by locally diffusing a p-type impurity layer into the silicon substrate; wherein the dummy resistor has its longitudinal direction set in <100> direction.
 17. A mechanical quantity measuring apparatus having formed in a surface of a single crystal silicon substrate: at least, a Wheatstone bridge circuit made up of a strain sensor and a dummy resistor; a conversion circuit to amplify a signal from the Wheatstone bridge circuit and convert it into a digital signal; a transmission circuit to transmit the digital signal to the outside of the silicon substrate; and a circuit to supply as electricity an electromagnetic wave energy received from the outside of the silicon substrate to any of the circuits; wherein the strain sensor has an n-type region formed by diffusing an n-type impurity layer into the silicon substrate; wherein the strain sensor has its longitudinal direction set in <100> direction wherein the dummy resistor has a region formed by diffusing an n-type impurity layer into the silicon substrate; wherein the dummy resistor has its longitudinal direction set in <110> direction.
 18. A mechanical quantity measuring apparatus having formed in a surface of a silicon substrate: at least, a Wheatstone bridge circuit made up of a strain sensor and a dummy resistor; a conversion circuit to amplify a signal from the Wheatstone bridge circuit and convert it into a digital signal; a transmission circuit to transmit the digital signal to the outside of the silicon substrate; and a circuit to supply as electricity an electromagnetic wave energy received from the outside of the silicon substrate to any of the circuits; wherein the strain sensor is formed of a p-type impurity diffusion layer and the dummy resistor is formed of an n-type impurity diffusion layer; wherein both of the strain sensor and the dummy resistor have their longitudinal directions set in <110> direction.
 19. A mechanical quantity measuring apparatus having formed in a surface of a single crystal silicon substrate: at least, a Wheatstone bridge circuit made up of a strain sensor and a dummy resistor; a conversion circuit to amplify a signal from the Wheatstone bridge circuit and convert it into a digital signal; a transmission circuit to transmit the digital signal to the outside of the silicon substrate; and a circuit to supply as electricity an electromagnetic wave energy received from the outside of the silicon substrate to any of the circuits; wherein the strain sensor is formed of an n-type impurity diffusion layer and the dummy resistor is formed of a p-type impurity diffusion layer; wherein both of the strain sensor and the dummy resistor have their longitudinal directions set in <100> direction.
 20. A mechanical quantity measuring apparatus having formed in a main surface of a single crystal silicon substrate a Wheatstone bridge circuit made up of a strain sensor and a dummy resistor; wherein the single crystal silicon substrate is formed at a back of its main surface with a bonding surface for bonding to an object to be measured.
 21. A mechanical quantity measuring apparatus according to claim 20, wherein the single crystal silicon substrate is 100 μm or less thick.
 22. A mechanical quantity measuring apparatus according to claim 20, wherein a visible mark is formed in a strain measuring direction.
 23. A mechanical quantity measuring apparatus having formed in a surface of a single crystal silicon substrate: a Wheatstone bridge circuit made up of a strain sensor and a dummy resistor; and a temperature sensor.
 24. A mechanical quantity measuring apparatus having formed in a main surface of a single crystal silicon substrate a Wheatstone bridge circuit made up of a strain sensor and a dummy resistor; wherein the strain sensor has in the silicon substrate a region into which a p-type impurity layer is diffused; wherein the strain sensor has its longitudinal direction set in <110> direction; wherein the dummy resistor has in the silicon substrate a region into which a p-type impurity layer is diffused; wherein the dummy resistor has its longitudinal direction set in a direction perpendicular to the strain sensor.
 25. A mechanical quantity measuring apparatus having formed in a main surface of a single crystal silicon substrate a Wheatstone bridge circuit made up of a strain sensor and a dummy resistor; wherein the strain sensor has in the silicon substrate a region into which an n-type impurity layer is diffused; wherein the strain sensor has its longitudinal direction set in <100> direction; wherein the dummy resistor has in the silicon substrate a region into which an n-type impurity layer is diffused; wherein the dummy resistor has its longitudinal direction set in a direction perpendicular to the strain sensor. 